Structural reconstruction and selective extraction of vanadium and chromium driven by calcium modification in the sodic roasting of high chromium vanadium slag

High-chromium vanadium slag, a typical hazardous solid waste, serves as a critical raw material for the comprehensive utilization of vanadium and chromium resources. To achieve synergistic recovery of vanadium and chromium, this study proposes an innovative process based on mineral phase reconstruction. A ternary eutectic multi-reaction system was established, and a novel Na 2 CO 3 -CaO co-roasting-leaching method was developed to enable selective separation of V and Cr. Combining DFT calculations, pure mineral roasting experiments, and actual vanadium slag roasting validation, the transformation mechanisms were elucidated: vanadium was converted into water-insoluble NaCaVO 4 and CaVO 3 , while chromium existed as water-soluble Na 2 CrO 4 during the Na 2 CO 3 -CaO co-roasting process. Under optimized conditions (roasting temperature 900 °C, duration 90 min, molar ratio n(CaO)/n(Na 2 CO 3 ) = 1), the average leaching efficiencies reached 84.23 % for Cr in the first-stage water leaching and 86.52 % for V in the second-stage ammonium bicarbonate leaching. The Cr concentration in the water leaching solution was 4.1 g/L (V: 0.7 g/L), whereas the V concentration in the ammonia leaching solution significantly increased to 7.1 g/L (Cr: 0.8 g/L). Impurity ions (Fe, Mn, Ti, Si) in both leaching solutions remained below 0.05 g/L. The remarkably low impurity levels substantially reduced purification costs, and the distinct concentration differences between V and Cr highlighted the selective separation advantages of the proposed process. These integrated characteristics provide critical feasibility support for industrial-scale implementation.